The present invention relates to a measuring instrument for determining the relative position of two objects, and in particular to an improved photoelectric digital length or angle measuring instrument.
A wide range of digital measuring instruments are known to the art. In general, such instruments measure a length or an angle in terms of discrete divisions or intervals formed on a precision scale, and in order to maximize the precision of the measurement it is often desirable to utilize intervals which are as small as possible. However in instruments which use counters to count the number of intervals associated with a measurement, a reduction in the size of the measurement interval will bring with it a concomitant increase in the counting speed of the counter. The precision or resolution of such instruments is limited, therefore, by either the grid constant of the precision scale which is used or the maximum counting speed of the counter.
One class of measuring instruments known to the art utilizes electronic means for subdividing the measurement interval to increase the precision or resolution of the instrument. However, the number of subdivisions provided by prior art instruments is, in practice, quite limited, for the cost and complexity of the circuitry used to properly combine the subdivisions of the measurement intervals with the counted intervals has in the past increased as a function of the number of subdivisions.